Steel wires for reinforcing rubber articles to be used as wires or the like for steel cords for tire reinforcement have conventionally been brass-plated steel wires having a brass-plating layer formed on their surface. These brass-plated steel wires are fabricated by cold-drawing a steel wire material, having been heat-treated by patenting or the like and brass-plated, to a predetermined wire diameter.
As for adhesiveness between brass-plated steel wire and rubber, it is known, for instance, that in the vulcanization (curing) process of tire production, an adhesion layer is formed when the steel wire is heated in contact with rubber and thereby sulfur in the rubber reacts with copper in the brass plating. And properties required of this adhesion layer are such that the adhesion layer must be formed quickly and reliably in the vulcanization process (initial adhesion performance) and the adhesion layer must not deteriorate due to moisture or heat during the use of the rubber article (adhesion durability performance).
Conventionally known methods for improving adhesion of brass-plated steel wire for reinforcing rubber articles to rubber include a method for alloying the surface layer by adding an alloy element, such as Fe or Ni, to the plating components (see References 1 and 2, for instance), a method for surface-treating by performing a plasma irradiation on the brass-plated steel wire (see Reference 3, for instance), a method for controlling the oxygen rate in the topmost surface of the plating layer (see Reference 4, for instance), and a method of performing a blast finishing after wire drawing (see Reference 5, for instance).    Reference 1: Japanese Unexamined Patent Application Publication No. 8-209386    Reference 2: Japanese Unexamined Patent Application Publication No. 2002-13081    Reference 3: Japanese Unexamined Patent Application Publication No. 2003-160895    Reference 4: Japanese Unexamined Patent Application Publication No. 2004-68102    Reference 5: Japanese Unexamined Patent Application Publication No. H5-278147